Atomic-scale deformation mechanisms in metal nanocomposites with intragranular amorphous nanoparticles

Dispersion strengthening, a well-established approach for enhancing the mechanical properties of metallic materials, typically utilizes crystalline dispersions, such as intermetallic or ceramic particles. Recent studies have shown that copper-based nanocomposites reinforced with intragranular amorphous B4C nanoparticles, fabricated via additive manufacturing, exhibit significantly improved strength and ductility. In this study, we employ molecular dynamics (MD) simulations to investigate the atomic-level mechanisms responsible for the enhanced mechanical performance of these nanocomposites. Compared to crystalline dispersions, the intragranularly dispersed amorphous B4C nanoparticles exhibit superior dislocation absorption and emission capabilities, owing to their inherent free volume and structural disorder. As a result, the surrounding copper matrix experiences reduced stress concentration and is better able to absorb and distribute strain energy, thereby delaying failure. Notably, the amorphous nanoparticles undergo densification during deformation via bond-switching and shear transformations in relatively loosely packed local regions, which contributes to the higher strain hardening rate. The dislocation dynamics predicted by MD simulations are validated through in-situ transmission electron microscopy experiments, and the strain-hardening behavior is consistent with prior experimental findings. This work provides a physical foundation for improving the mechanical properties of metallic materials through the use of amorphous dispersions.